There is provided a method of optimizing Rate Distortion Optimization candidate assessment in hardware apparatus, comprising determining which Rate Distortion Optimization candidates out of a plurality of candidates are separately processable, determining a processing delay of critical portions of candidate assessment hardware, determining a rule set governing how the separately processable candidates may be ordered for processing, determining an optimized processing order for processing the separately processable candidate assessments, dependent on the processing delay of critical portions of the candidate assessment hardware and the determined rule set, and processing the candidates according to the determined processing order. There is also provided an apparatus for carrying out the improved Rate Distortion Optimization method.